Drop In

v. visit informally or uninvited, briefly visit to say hello

Drop-In was a Canadian television series for youth broadcast on CBC Television from 28 September 1970 to 1974. Various hosts were featured throughout the course of the series to present a variety of topics.The show was broadcast three times per week in the 1970-1971 season. This was increased to four times per week in the following year.
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Verb
1. visit informally and spontaneously; "We frequently drop by the neighbors' house for a cup of coffee"
(synonym) drop by, come by
(hypernym) visit, call in, call

[analogy with drop-outs] Spurious characters appearing on a terminal or console as a result of line noise or a system malfunction of some sort. Especially used when these are interspersed with one's own typed input.
[Jargon File]

visitor, one who drops in He was a drop-in at the Seniors' Centre. He liked to go there.